Background
Nigella sativa L., commonly known as black seed, belongs to the botanical family Ranunculaceae. It has being used in countries bordering the Mediterranean Sea, Pakistan, India and Iran, as a natural remedy for over 2000 years [
1]. Black seed components display a remarkable array of biochemical, immunological and pharmacological actions, including bronchodilatory [
2], anti-inflammatory [
3], antibacterial [
4], hypoglycaemic [
5] and immunopotentiating effects [
6].
N. sativa extract has been shown to possess immunopotentiating, anti-oxidant, anti-tumoral, and anti-diabetic properties. The oil of
N. sativa exhibits analgesic and anti-inflammatory effects in rats. Most of these properties have been attributed mainly to the quinone constituents of
N. sativa, of which thymoquinone is the main active ingredient of the volatile oil isolated from the black seeds. Thymoquinone has been shown to possess strong antioxidant properties and to suppress the expression of inducible NO synthase in rat macrophages [
7].
Many studies have also examined the anti-diabetic effect of
N. sativa in diabetic animal models. Aside from the effect of its crude aqueous extract to restore glucose homeostasis.
N. sativa petroleum ether extract significantly lowered fasting plasma levels of insulin and triglycerides and normalized HDL-cholesterol. In this latter study by Le and collaborators,
N. sativa was also shown to enhance liver cell insulin sensitivity [
1,
3,
7].
β cell defect and insulin resistance are essential features of non-insulin-dependent diabetes mellitus (NIDDM) and both features are the focus of intensive investigations. In this context, plants are source of many biochemical substances that present interesting therapeutic properties. Some plants with anti-diabetic properties have been in use in many Middle Eastern countries as a natural remedy for diabetes in traditional medicine;
N. sativa is one of these plants. It has a great potential in the treatment of diabetic animals because of its combined hypoglycemic [
2,
4,
7].
In earlier experiments we have shown that streptozotocin, given at 45 days post-infection (dpi) affected the morphology of the reproductive organs of male and female worms and lowered the number of viable eggs in the intestine and the amount of eggs in the feces. However, the morphological changes were caused directly by the drug [
5‐
7].
STZ, an antibiotic produced by Streptomyces achromogenes, is the most commonly used agent in experimental diabetes. The mechanism by which STZ destroys β-cells of the pancreas and induces hyperglycemia is still unclear. Many actions have been attributed to STZ that are similar to those that have been described for the diabetogenic action of alloxan, including damage to pancreatic β-cell membranes and depletion of intracellular nicotinamide adenine dinucleotide (NAD) in islet cells. In addition, STZ has been shown to induce DNA strand breaks and methylation in pancreatic islet cells [
8,
9]. Its diabetogenic action has been ascribed to an increase in the intracellular methylation reaction, DNA strand breaks, and the production of nitric oxide (NO) and free radicals.NO is involved in pancreatic destruction, where the interaction between NO and ROS modulates oxidative damage. STZ can be used to induce different types of diabetes. For example, to produce experimental models of Type 1 diabetes, mice are treated with high doses of STZ, which depletesb -cells [
8,
10,
11].
It is known that people suffering from diabetes mellitus are related to higher incidence of bacterial and fungal infections. Diabetes Mellitus is a chronic disease which affects the metabolism of proteins, carbohydrates and lipids. The major characteristic is hyperglycaemia as a consequence of abnormal secretion of insulin in the pancreas (type I) or inefficient action of insulin in the target tissues (type II) [
12]. Type 2 diabetes is sharply increasing globally, including in many parts of the developing world, in major part as a consequence of the worldwide “epidemic” of obesity. For centuries, prior to and after the discovery of insulin, medicinal plants have been used to normalize glycemia in diabetic patients. This disorder promotes adverse effects in all organic systems. Diabetes exerts a negative action on the neuroendocrine axis and those effects can enhance the action of diabetes on other organs that are dependent on the axis [
12].
Diabetics and experimental animal models of diabetes exhibit high oxidative stress due to persistent and chronic hyperglycemia, which may deplete the activity of the anti-oxidative defense system and promote the generation of free radicals [
12]. Streptozotocin (STZ) is frequently used to induce diabetes in experimental animals through its toxic effects on pancreatic β -cell [
13] and as a potential inducer of oxidative stress. It has been reported that diabetes induced by STZ is the best characterized system of xenobiotic-induced diabetes and the commonly used model for the screening of anti-hyperglycemic activities [
14].
The present study was designed to investigate the mechanism(s) of the hypoglycaemic effect of N. sativa hydroalcholic extract, especially with respect to hepatic gluconeogenesis, and to investigate its possible streptozotocin effects in diabetic rats.
Discussion
Diabetes mellitus is a chronic, systemic, metabolic disease defined by hyperglycemia and characterized by alterations in the metabolism of carbohydrate, protein and lipid. Oxidative stress thought to be increased in a system where the rate of free radical production is increased and/or the antioxidant mechanisms are impaired. In recent years, the oxidative stress-induced free radicals have been implicated in the pathology of insulin dependent diabetes mellitus [
3,
5,
8‐
10].
In our study, a significant weight loss was observed in the diabetic group while NS treated (5 mg/kg b.w.) rats exhibited significant increase in the BW in comparison to diabetic group (Group 2) but was lower than in the normal controls. This effect on the BW was not observed at higher doses of extract. This finding is in agreement with Kanter et al., 2004 reported that NS markedly improved BW gain in STZ-induced diabetic rats. A possible explanation for this might be that NS reduces hyperglycemia, and therefore protein wasting due to inaccessibility of carbohydrate does not occur [
17].
In present study, the hydroalcholic extract of NS at dose of 5 mg/kg b.w. revealed a significant hypoglycemic effect in STZ-induced diabetic rats by diminishing the FBG levels. The FBG lowering effect of that was further increased after 32 day treatment. In addition, results showed that the anti-hyperglycemic effect of the NS extract is time dependent. This finding is in agreement with Fararh et al., 2002 [
18].
In present study, the lowering effects of black seed oil on blood glucose were correspondent with the previous trials. Some studies have been conducted on the characterization of the bioactives and mechanisms mediating its anti-hyperglycemic action. In an experimental study, Alsaif [
19] reported that blood glucose lowering effect of black seed oil was due to improved insulin insensitivity in diabetic rats. Another study proposed its hypoglycemic effect is due to improved extrapancreatic actions of insulin rather than by stimulated insulin release [
20]. Furthermore, Abdelmeguid et al. [
21] reported that the anti-hyperglycemic effect of black seed oil and its active component thymoquinone could be due to reduction of oxidative stress, thus preserving pancreatic β -cell integrity lead to insulin levels increase. Furthermore, the black seed oil contains many bioactive constituents such as thymoquinone, p-cymene, pinene, dithymoquinone and thymohydroquinone [
22].
The increase in glycogen levels could be due to the antidiabetic activity of NS, streptozotocin induces degeneration of the pancreas with a lobular atrophy and a decline in size and number of Langerhans islets [
23,
24]. In this study, the damage of pancreas in STZ treated diabetic rats and regeneration of Langerhans islets by NS extract was observed. Furthermore, the number of islets, islet cells and islets diameter significantly increased in NS (5 mg/kg b.w.) treated group compared to STZ-induced diabetic group. However, there have been no morphometric studies to date examining the pancreatic structure in STZ-diabetic rats treated with NS extract. Histopathlogically, treatment with the hydroalcholic extract of NS (5 mg/kg b.w.) revealed partial regeneration of the islet cells with light hydropic degeneration and necrosis in the remaining cells. These findings are in accordance with the results reported by Kanter et al. [
17].
Measurement of the effect of
N. sativa on gluconeogenesis and liver glucose production helps to clarify part of the hypoglycemic mechanism since hepatic glucose production through gluconeogenesis is known to contribute to hyperglycemia in diabetic patients. Research on isolated hepatic cells showed a significant decrease in glucose production from gluconeogenic elements like glycerol, alanine and lactate in
Nigella sativa oil-treated animals as compared to the untreated animals [
3‐
5]. This significant decrease in liver glucose output and ameliorative effect on regeneration of pancreatic islets suggests that the observed antidiabetic action of
N. sativa is at least partially mediated through an effect on hepatic gluconeogenesis.
Conclusions
In conclusion, based on the experimental findings, it was suggested that administration of N. sativa, at a safe dose level, suppresses STZ-induced diabetic in the rat. We believe that further preclinical research into the utility of N. sativa treatment may indicate its usefulness as a potential treatment in diabetic patients, our results suggested that hydroalcholic extract of NS at low doses has beneficial effect on FBG level and ameliorative effect on regeneration of pancreatic islets and may be used as a therapeutic agent in the management of diabetes mellitus.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
SA and RH participated in the histopathological evaluation, performed the literature review, acquired photomicrographs and drafted the manuscript and gave the final histopathological diagnosis and designed and carried out all the experiments. JJ is the principal investigator of the laboratory in which the research was performed and contributed to the interpretation of the data and writing of the manuscript. DKH, RM, FKH, MT and HA edited the manuscript and made required changes and wrote the manuscript. All authors have read and approved the final manuscript.